In buildings, energy consumed in heating and cooling occupies about 25 percent of total energy consumption.
Further, energy loss through windows and doors reaches about 35% of the total energy consumption. This is because the windows and doors have a coefficient of overall heat transmission 2 to 5 times higher than those of walls or roofs and are thus the weakest part of an outer cover of the building in terms of thermal insulation. Accordingly, it has been required to develop windows and doors excellent in thermal insulation with a coefficient of overall heat transmission similar to those of the walls in terms of nationwide energy conservation as well as energy conservation in buildings.
In general, a window or door includes a frame forming a shape of the window or door, and a glass sheet coupled to the frame. In the window or door, thermal energy generally leaks through the glass sheet that occupies the largest area of the window or door. Accordingly, a vacuum glass capable of significantly reducing leakage of thermal energy has been spotlighted.
A vacuum glass includes a vacuum layer between two panes and can minimize thermal loss due to conduction, convection and radiation of gas when used together with a low-E glass.
In the vacuum glass, a pillar for maintaining a distance between the panes is used to form the vacuum layer. Since the vacuum glass is configured to have the vacuum layer in an inner space, external force can be applied to the panes due to difference in pressure between an inner space under a vacuum and an outer space under atmospheric pressure. External force applied to the panes is concentrated on a portion of the pane adjoining the pillar, and acts as stress.
Typically, the pillars are densely arranged in a square shape in order to distribute stress. However, dense arrangement of the pillars causes deterioration in thermal insulation due to thermal conduction of many pillars.
Further, if an arrangement distance in the square shape is increased in order to reduce the number of pillars causing degradation of thermal insulation, stress applied to the vacuum glass increases and can cause breakage of the vacuum glass during manufacture, transport and use of the vacuum glass.